The rotameters comprising a vertically disposed tapered flow passage including a float suspended therein, wherein the vertical position of the float relative to a reference section located at the bottom inlet extremity of the tapered flow passage indicates the amount of flow rate, are widely employed in industries and scientific laboratories, which provide flow measurement with excellent accuracy and reliability. There are a number of short-comings in the existing versions of the rotameters which are, firstly, the lack of an accurate and reliable electronic read-out device incorporated into the rotameter that provides the information on the flow rate in the form of an electrical signal which can be fed into flow computers or flow control devices, and secondly, measuring flow of different fluids requires different rotameters custom calibrated to the specific fluid under measurement and, consequently, no rotameter available at the present time is capable of measuring flow of fluid with varying density.